Almost all chemical reactions absorb or release heat. this is because

..Chemical reactions involve the breaking and formation of chemical bonds. The breaking of the bonds is usually an endothermic process while the formation of bonds is usually an exothermic process. The net cumulative effect (the difference between the energy levels of products and products in the reaction) makes the reaction overall endothermic or exothermic.

a: 45.9 meters

b: 4.29 seconds

step-by-step explanation:

a: h(t)=1/2(-9.8)(3)^2+0(3)+90

h(t)=-4.9(3)^2+90

h(t)=-44.1+90

h(t)=45.9 meters

b: 0=1/2(-9.8)(t^2)+0t+90

0=-4.9t^2+90

-90=-4.9t^2

18.37=t^2

t=4.29 seconds

in the second question, the numbers aren't exact, but they're a close approximation.